Ground-penetrating radar (GPR) is a geophysical method that uses radar pulses to image a subsurface. This is a non-destructive method of imaging. The non-destructive method uses electromagnetic radiation in the radiowave band (HF/VHF/UHF frequencies) of the radio spectrum, and receives the reflected signals from subsurface structures. The amplitude and phase of the reflected signal depends on changes in the structure's physical properties. GPR can be used in different applications in a variety of media, including rock, soil, ice, fresh water, pavements and buildings. It can detect objects and changes in material, for example subsurface voids, cavities and utilities.
The depth range of GPR is limited by the electrical conductivity of the ground, the transmitted center frequency, the radiated power and receiver sensitivity. As conductivity increases, the penetration depth also decreases. This radiated energy is more quickly converted into heat. For each wavelength in the ground, a certain fraction of the energy is lost causing a loss in signal strength at depth. Typical depth performance of GPRs is about 20 wavelengths. Higher frequencies, with shorter wavelengths, do not penetrate as far as lower frequencies, but give better resolution. In conventional systems, good penetration is achieved in dry sandy soils or dense dry materials such as granite and limestone where the depth of penetration could be up to 50 m. In moist and/or clay-laden soils and soils with high electrical conductivity, penetration is sometimes only a few centimeters.
In conventional low frequency GPR, antennas require long wires with resistors at regular intervals. In these conventional antennas, the resistors are placed in series with the antenna segments in order to dampen the antenna and provide a resistive load. The electronics and batteries are placed in the middle of the antenna. Such an arrangement makes the antennas fragile and costly to manufacture.
It is also noted that the quality of land seismic data suffers from irregularities within the near surface, which is composed of layers that have experienced variable degrees of weathering. Examples of these irregularities include: lateral variation in thickness, lateral and vertical velocity variations, rugged topography, sand dune structures, and effects of near-surface water. The effects of these irregularities on seismic data include: static, scattering, multiples, ground roll, weak penetration of signal into deeper layers, and severe amplitude losses. These effects on seismic data are more severe in arid areas due to the extensive weathering that these areas have experienced during their geological history. Therefore, petroleum companies, for example, working with seismic data in Middle Eastern countries find that these data suffer greatly from adverse near-surface effects. This can be evidenced by the increasing number of forums devoted to issues of the near-surface during the last few years.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.